Aromatic hydrocarbon separation process



July 10, 1956 R. o. sHELToN AROMATIC HYDROCARBON SEPARATION PROCESSFiled NOV. 5, 1951 ATTORNEYS Unted rates Patent AROMATIC HYDROCARBONSEPARATION PRCESS Russell 0. Shelton, Bartlesville, Okla., assigner toPhillips Petroleum Company, a corporation of Delaware ApplicationNovember 5, 1951, Serial No. 254,915

7 Claims. (Cl. 260-674) This invention relates to improvements in theseparation of aromatic hydrocarbons from a petroleum fraction and to therecovery or" substantially pure aromatic hydrocarbons from admixtureswith non-aromatic hydrocarbons. In one of its aspects this inventionrelates to a method employing solvent extraction for the recovery of anaromatic hydrocarbon concentrate from a cracked gasoline containingaromatic hydrocarbons and olenic hydrocarbons. In still another of itsaspects this invention is directed to a method for the recovery of anaromatic concentrate suitable for use as a blending stock by solventextraction of a cracked gasoline, such as a catalytically crackedgasoline, containing substantial amounts of aromatic and olenichydrocarbons. In still another of its aspects this invention relates tothe solvent extraction of a cracked gasoline containing substantialamounts of oleinic and aromatic hydrocarbons with a liquid selectivesolvent for aromatic hydrocarbons.

In the production of gasoline or other low boiling hydrocarbons fromcrude oil or from a suitable cracking stock there is produced inadmixture With parafiinic, eletinic and naphthenic hydrocarbonssubstantial amounts of aromatic hydrocarbons. By fractional distillationthe aromatic hydrocarbon content can be increased up to about 50 percent or more depending upon the composition of the petroleum fractionbeing separated. Furthur concentration by distillation to produce asubstantially pure aromatic fraction is often impractical and for thisreason further concentration of the aromatic hydrocarbons is usuallyaccomplished by selective solvent extraction or by extractivedistillation, employing in each instance a liquid selective solvent forthe aromatic hydrocarbons. In a selective solvent extraction operationfor the recovery of aromatic hydrocarbons it has been found that thepresence of substantial amounts i. e. above about 50 per cent by volumetotal aromatic and olenic hydrocarbons cause the hydrocarbon fractionbeing treated to be miscible with the selective solvent, or at least tohinder phase separation. In order to obtain phase separation in such aselective solvent extraction operation a low temperature must frequentlybe employed.

In accordance with the present invention a petroleum fraction containingaromatic hydrocarbons and olelinic hydrocarbons is subjected to solventextraction with a liquid selective solvent for aromatic hydrocarbons inthe presence of a relatively high boiling petroleum fraction. In myinvention I extract a light cracked gasoline containing oletinic andaromatic hydrocarbons With a liquid selective solvent for aromatichydrocarbons, such as sulfur dioxide, furfural, nitrobenzene, phenolsand the like, in the presence of a high boiling petroleum fraction, suchas a gas-oil, which is suitable for use as a cracking stock for theproduction of the aforementioned light cracked gasoline. The addition ofa high boiling petroleum fraction to the solvent extraction operationpromotes phase separation in that it reduces the miscibility of theselective solvent in the particular petroleum fraction being treated forthe recovery of an aromatic concentrate. The pres- Patented July l0,1956 ent invention Will be better understood by referring to theaccompanying drawing which is a ilow plan schematically illustrating apreferred embodiment of my invention.

Referring now to the drawing numeral 11 designates a feed line throughwhich a light cracked gasoline boiling in the range -475 F. andcontaining olenic and aromatic hydrocarbons is introduced into extractor12. Extractor 12 may be any type of suitable contacting device for aliquid-liquid solvent extraction operation and may comprise acombination of mixer-settler or a continuous contacting column. Into oneend of extraction zone 12 is introduced via line 1 a liquid selectivesolvent for aromatic hydrocarbons such as sulfur dioxide. Into the otherend of the extraction zone 12 a suitable high boiling petroleum fractionsuch as a gas oil boiling in the range S50-950 F. and suitable for useas a cracking stock and preferably low in aromatic hydrocarbons, usuallybelow about l0 per cent by volume, is introduced via line 14. Thesolvent extraction operation carried out within extraction zone 12 maybe concurrently or countercurrently. As shown in the accompanyingdrawing a countercurrent solvent extraction operation is being carriedout. From one end of extraction zone 12 a raftinate phase is Withdrawnvia line 16 and from the other end of extraction zone 12 an extractphase is withdrawn via line 18. Line 16 leads to a suitable separatingor fractionating device such as flash tank 19 wherein sulfur dioxide isashed and removed via line 2l). From the bottom of ilash tank 19 isremoved via line 21 the remaining ratnate phase, now substantially freeof sulfur dioxide, which is then passed to ranate fractionator 22,Within ralinate ractionator 22 the rainate phase is subjected tofractional distillation and a rainate product is removed overhead vialine 23. From the bottom of fractionator 22 is removed via line 24 abottoms fraction consisting substantially of the higher boilingpetroleum fraction which was introduced into extraction zone 12 via line14.

The extract phase removed from extraction zone 12 via line 18 is passedinto a suitable separating or fractionating device such as ash tank 26.Sulfur dioxide is removed via line 28 by flashing. From the bottom offlash tank 26 is recovered via line 29 the remaining extract phase whichis then passed into extract fractionator 30. An extract product isrecovered overhead from fractionator 30 via line 31. The extractrecovered via line 31 is an aromatic hydrocarbon concentrate and issubstantially enriched with respect to aromatic hydrocarbons over thearomatic hydrocarbon content found in the feed which was introduced intoextractor 12 via line 11. From the bottom of fractionator 30 is removedvia line 32 the remaining portion of the high boiling petroleum fractionintroduced into extractor 12 via line 14. The portions of the highboiling petroleum fraction in line 32 and 24 are admixed in line 33 andthen introduced into a cracking zone 34. Cracking zone 34 may be anysuitable cracking zone either catalytic or noncatalytic, if catalytic,either a fixed, moving or iiuidized bed catalytic cracking zone.Associated with cracking Zone 34 are various separation zones andequipment, not shown, such as fractionators, extractors, etc. The heavyproducts from the cracking Zone 34 and its accompanying separation zonesare removed via line 36 and a light cracked gasoline fraction is removedvia line 11 to feed extractor 12.

One advantage of operating in accordance with the present invention isthat the high boiling petroleum fraction used as a stripping medium withextractor 12 and recovered later on can be used as a cracking stock.This is particularly desirable since impurities tend to build up in thestripping medium if the stripping medium were to be recycled within theprocess. According to my invention however, the recovered strippingmedium or higher boiling petroleum fraction is passed directly to acracking operation wherein any impurities or undesirable constituentssuch as sulfur compounds which may have been picked up during thesolvent extraction step are destroyed or cifectively removed.

In a typical operation in accordance with the present invention apetroleum fraction such as a light cracked gasoline having Ya boilingrange ofY 114 F.-430 F. and containing about 30 per cent by volumeparaflins, 5l per cent by volume olenic hydrocarbons, 8 per cent byvolume naphthenic hydrocarbons and 11 per cent by volume aromatichydrocarbons is solvent extracted with liquid sulfur dioxide. Sulfurdioxide is supplied at a rate of 4.88 (about pounds per pound ofgasoline feed. The higher boiling petroleum fraction such as a gas oilhaving a boiling range within 600 F.900 F. and which is suitable for useas a cracking stock in a catalytic or non-catalytic cracking operation,is introduced as a stripping oilY at the bottom of the extractor at therate of 1.11 (about l) pound per pound of gasoline feed. This higherboiling petroleum fraction is preferably low in aromatic hydrocarboncontent, preferably less than per cent by volume since aromatichydrocarbons are undesirable in a catalytic cracking stock. Thetemperature in the extractor may be in the range 0-70 F., preferablybetween -30 F. The pressure within the extractor may range from 30-70 p.s. i. g., preferably about 40 p. s. i. g. but sulcient to maintain thesulfur dioxide in the liquid phase. The raiiinate phase removed from theextractor comprises 0.48 pound sulfur dioxide, 0.98 pound stripping oiland 0.63 pound of hydrocarbons in the gasoline boiling range, all on thebasis of 1 pound of gasoline feed. One or more stages of ashing may beemployed to separate the SO2 from the hydrocarbons, or the separationmay be made more completely by fractionation. The remaining hydrocarbonsafter SO2 removal are then fractionated to separate a rainate productfrom the stripping oil. The rainate product has a boiling range between128 F. and 438 F. and comprises 36 per cent by volume parainichydrocarbons, 44 per cent by Volume olenic hydrocarbons, 16 per cent byvolume naphthenic hydrocarbons and 4 per cent by volume aromatichydrocarbons. The extract phase removed from the extractor contains 4.40pounds of sulfur dioxide, 0.13 pound of stripping oil and 0.37 pound ofgasoline hydrocarbons, per pound of feed. After sulfur dioxide removalfrom the extract phase the light hydrocarbons are separated from thestripping oil by fractionation. An extract product is recovered having aboiling range within 130 F. and 425 F. and contains 6 per cent by volumeparainic hydrocarbons, 57 per cent by .volume olenic hydrocarbons, 8.per cent by volume naphthenic hydrocarbons and 29 per cent by volumearomatic hydrocarbons. The stripping oil streams recovered from therailinate and extract phases are then combined and employed as feed inthe cracking operation for the production of additional feed.

The data set forth in the foregoing operation were obtained without theuse of an enriching section in the extractor, the feed and sulfurdioxide merely being mixed and introduced into the stripping section.With the use of an enriching section the aromatic hydrocarbon content ofthe rainate would have been reduced considerably and the concentrationof aromatic hydrocarbons in the extract would have been increased.

The petroleum fraction which is advantageously solvent extracted inaccordance with the process of this invention to produce an aromaticconcentrate is preferably a gasolinev boiling range hydrocarbon materialsuch as a cracked gasolinehaving a boiling range within 100 F. and 475F. The process of this invention is particularly applicableto. crackedgasoline which contains substantial amounts of aromatic and olenichydrocarbons, especially whereinv the total aromatic hydrocarbons andolenic hydrocarto obtain without resorting toy rather low temperaturesand other extreme undesirable conditions. The process of this inventionis particularly applicable to the treatment of a cracked gasolinefraction with which at a temperap ture within the range 0-770 F.,especially above 20 F.

phase separation between a selective solvent for aromatic hydrocarbons(such as SO2) and said cracked gasoline fraction is not obtainable.

The higher boiling petroleum fraction which is used as a strippingliquid in accordance with the process of my invention is preferably agas oil having a boiling range within 550 F. and 950 F. This higherboiling fraction is preferably substantially free of aromatichydrocarbons and is preferably suitable for use as a cracking stockeither in a catalytic or non-catalytic cracking operation.

As will be evident to those skilled in the art upon read-- ing thisdisclosure many substitutions, moditications and operational changes maybe made without departing from the spirit or scope of this disclosureand invention.

claim:

1. A process for the production of an aromatic hydrocarbon concentratefrom a light cracked gasoline containing above about 50 per cent byvolume olefinic hydrocarbons and aromatic hydrocarbons which comprisessolvent extracting in an extraction zone and light cracked gasoline witha selective solvent for aromatic hydrocarbons; introducing into saidextraction zone a higher boiling petroleum fraction substantially freeof aromatic hydrocarbons and having a boiling point range within 550 F.and 950 F.; extract phase and a raffinate phase; removing said selectiveSolvent and said higher boiling petroleum fraction from said extractphase to yield an extract substantially enriched with respect toaromatic hydrocarbons; subjecting the resulting removed higher boilingpetroleum fraction to cracking in a cracking zone and recoveringtherefrom a light cracked gasoline containing olenic hydrocarbons andaromatic hydrocarbons.

2. A process for the production of an aromatic hydrocarbon concentratefrom a light cracked gasoline having a boiling point range within F. and475 F. and wherein the aromatic hydrocarbon-olefinic hydrocarbon contentamounts to at least about 50% by volume which comprises solventextracting said light crackedV gasoline at a temperature in the range0-70 F. with liquid sulfur dioxide in the presence of a gas oil having aboiling point range within 550 F. and 950 F. and containing less than 10per cent by volume aromatic hydrocarbons; separately recoveringanextract phase and a raffinate phase; removing sulfur dioxide and saidgas oil from said extract phase to yield an extract substantiallyenriched with respect to aromatic hydrocarbons; subjecting the resultingremoved gas oil to cracking in a cracking zone and recovering therefroma light cracked gasoline containingV oleiinic hydrocarbons and aromatichydrocarbons.

3. A process for the production of an aromatic hydrocarbon concentratefrom a light cracked gasoline containing above about 50 per cent byvolume oleiinic hydrocarbons and aromatic hydrocarbons which comprisessolvent extractingl said light cracked gasoline with a selective solventfor aromatic hydrocarbons in the presence or" a higher boiling petroleumfraction containing less than l() per centr by volume aromatichydrocarbon and having a boilingpoint range within 550 F'. and 950 F.;separately recovering an extract phase and a rainate phase; removingsaid selective solvent and said higher separately recovering an boilingpetroleum fraction from said extract phase to yield-an extractsubstantially enriched with respect to aromatic hydrocarbons; subjectingthe resulting removed higher boiling petroleum fraction to cracking in acracking zone; recovering therefrom a light cracked gasoline containingolenic hydrocarbons and aromatic hydrocarbons and recyclinfy at least aportion of the recovered light cracked gasoline to the aforesaid solventextraction Step.

4. A process in accordance with claim 2 wherein gas oil is removed fromsaid raiinate phase subjected to cracking in said cracking zone alongwith the gas oil removed from said extract phase.

5. A process for the production of an aromatic concentrate from a lightcracked gasoline containing above about 50 per cent by volume oleiinichydrocarbons and aromatic hydrocarbons which comprises solventextracting said light cracked gasoline with a selective solvent foraromatic hydrocarbons in the presence of a higher boiling petroleumfraction having a boiling range Within 550 F. and 950 F. and containingless than 10 per cent by volume aromatic hydrocarbons; separatelyrecovering an extract phase and a raffinate phase; removing saidselective solvent and said higher boiling petroleum fraction from saidextract phase to yield an extract substantially enriched with respect toaromatic hydrocarbons; removing said selective solvent and said higherboiling petro leum fraction from said raffinate phase; subjecting thehigher boiling petroleum fraction removed from said extract and ranatephases to cracking in a cracking zone; and recovering from said crackingzone a light cracked gasoline containing olelinic hydrocarbons andaromatic hydrocarbons.

6. A process in accordance With claim 5 wherein at least a portion ofthe recovered light cracked gasoline is recycled to the solventextraction step.

7. A process for the production of an aromatic hydrocarbon concentratefrom a light cracked gasoline containing above about per cent by volumeolenic hydrocarbons and aromatic hydrocarbons which comprises solventextracting in an extraction zone said light cracked gasoline with aselective solvent for aromatic hydrocarbons; introducing into saidextraction zone a higher boiling petroleum fraction containing less than10 per cent by volume aromatic hydrocarbons and having a boiling pointin the range of 550 F. to 950 F.; separutely recovering an extract phaseand a rafnate phase; removing said selective solvent and said higherboiling petroleum fraction from said extract phase to yield an extractsubstantially enriched with respect to aromatic hydrocarbons; subjectingthe resulting removed higher boiling petroleum fraction to cracking in acracking zone and recovering therefrom a light cracked gasolinecontaining olefinic hydrocarbons and aromatic hydrocarbons.

References Cited in the lile of this patent UNITED STATES PATENTS2,064,842 Lowry et a1. Dec. 22, 1936 2,366,570 Souders et al. Jan. 2,1945 2,379,334 Atwell lune 26, 1945 2,380,853 Linn et al July 3l, 19452,410,166 Kimball Oct. 29, 1946 OTHER REFERENCES Francis: industrial andEng. Chem., vol. 36, pages 764-771 (August, 1944; 8 pages).

Francis: Industrial and Eng. Chem., vol. 36, pages 1096-1104 ,December1944; 9 pages).

Sachanen: Chemical Constituents of Petroleum (1945), page 201, Reinhold,N. Y., publishers.

1. A PROCESS FOR THE PRODUCTION OF AN AROMATIC HYDROCARBON CONCENTRATEFROM A LIGHT CRACKED GASOLINE CONTAINING ABOVE ABOUT 50 PER CENT BYVOLUME OLEFINIC HYDROCARBONS AND AROMATIC HYDROCARBONS WHICH COMPRISESSOLVENT EXTRACTING IN AN EXTRACTION ZONE AND LIGHT CRACKED GASOLINE WITHA SELECTIVE SOLVENT FOR AROMATIC HYDROCARBONS; INTRODUCING INTO SAIDEXTRACTION ZONE A HIGHER BOILING PETROLEUM FRACTION SUBSTANTIALLY FREEOF AROAMTIC HYDROCARBONS AND HAVING A BOILING POINT RANGE WITHIN 550* F.AND 950* F.; SEPARATELY RECOVERING AN EXTRACT PHASE AND A RAFFINATEPHASE; REMOVING SAID SELECTIVE SOLVENT AND SAID HIGHER BOILING PETROLEUMFRACTION FROM SAID EXTRACT PHASE TO YIELD AN EXTRACT SUBSTANTIALLYENRICHED WITH RESPECT TO AROMATIC HYDROCARBONS; SUBJECTING THE RESULTINGREMOVED HIGHER BOILING PETROLEUM FRACTION TO CRACKING IN A CRACKING ZONEAND RECOVERING THEREFROM A LIGHT CRACKED GASOLINE CONTAINING OLEFINICHYDROCARBONS AND AROMATIC HYDROCARBONS.